Come to think of it, perhaps I should explain why I think there will be a long-term downward trend.
Given that every large, complex civilization before ours has eventually collapsed, the burden of proof should be on those who claim that ours is exceptional and will not collapse. If I'm wrong and our civilization outlives me, I don't mind losing some money on my investments. I'd rather be a poor guy in a rich civilization if this insures me against being a poor guy in a poor civilization. If I'm right, I want to at least use the fact that I'm right to extract some wealth as a consolation prize and use that wealth to help myself and other techno-geeks survive and perhaps somehow hasten the next civilizational cycle.
If I had to guess, the most likely cause of collapse would be dwindling oil and gas supply combined with a growing demand caused by population growth and increasing industrialization. It's true that this creates incentives to develop alternative energy sources, but there are organizational, informational, and physical limitations on how quickly our infrastructure can be retooled to such alternatives. It is prudent to hedge one's bets that engineers and entreprneurs will win this race. Furthermore, every single alternative has a higher per-kilojoule cost than oil. Therefore, even if liquified coal, or biodiesel, or fuel cells become commercially viable, we will still be spending a larger fraction of our wealth just keeping the lights on than we do now, and I would expect the effect on the economy to be similar to a tax corresponding to the same amount.
But that's just my guess. I don't claim to know why our civilization will collapse, nor when this will happen. I do know that this collapse will not happen overnight, and there may be a long time window during which to exploit it before "the market is at 0".
I have no crystal ball with which to predict the Future, a confession that comes as a surprise to some journalists who interview me. Still less do I think I have the ability to out-predict markets. On every occasion when I've considered betting against a prediction market - most recently, betting against Barack Obama as President - I've been glad that I didn't. I admit that I was concerned in advance about the recent complexity crash, but then I've been concerned about it since 1994, which isn't very good market timing.
I say all this so that no one panics when I ask:
Suppose that the whole global economy goes the way of Japan (which, by the Nikkei 225, has now lost two decades).
Suppose the global economy is still in the Long Slump in 2039.
Most market participants seem to think this scenario is extremely implausible. Is there a simple way to bet on it at a very low price?
If most traders act as if this scenario has a probability of 1%, is there a simple bet, executable using an ordinary brokerage account, that pays off 100 to 1?
Why do I ask? Well... in general, it seems to me that other people are not pessimistic enough; they prefer not to stare overlong or overhard into the dark; and they attach too little probability to things operating in a mode outside their past experience.
But in this particular case, the question is motivated by my thinking, "Conditioning on the proposition that the Earth as we know it is still here in 2040, what might have happened during the preceding thirty years?"
There are many possible answers to this question, but one answer might take the form of significantly diminished investment in research and development, which in turn might result from a Long Slump.
So - given the way in which the question arises - I know nothing about this hypothetical Long Slump, except that it diminished investment in R&D in general, and computing hardware and computer science in particular.
The Long Slump might happen for roughly Japanese reasons. It might happen because the global financial sector stays screwed up forever. It might happen due to a gentle version of Peak Oil (a total crash would require a rather different "investment strategy"). It might happen due to deglobalization. Given the way in which the question arises, the only thing I want to assume is global stagnation for thirty years, saying nothing burdensome about the particular causes.
What would be the most efficient way to bet on that, requiring the least initial investment for the highest and earliest payoff under the broadest Slump conditions?